TWO MECHANICS REPORT ON EVENTS THAT CONTRIBUTED TO A CRASH AX NOT BEING TRANSFERRED FROM A REMOVED FIRST OFFICER'S SEAT TO THE NEW REPLACEMENT SEAT ON AN ATR72. THE AIRCRAFT WAS DELAYED AT A DOWNLINE STATION UNTIL ANOTHER AX WAS LOCATED.

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ON THE NIGHT OF OCT/XA/08 ACFT HAD AN MEL CLRED; FO SEAT R-HAND ARMREST BROKEN; THE REPLACEMENT OF THE FO'S SEAT WAS DECIDED AND THE FO'S SEAT REPLACED. THE CRASH AX THAT GOES BEHIND THE SEAT WAS NOT INSTALLED. I AND MY CO-WORKER WERE ASSIGNED THIS TASK; OF REPLACING THE FO'S SEAT. WE BOTH FOLLOWED THE PROCS AND WE HAD QUALITY CTL VERIFY AND INSPECT THE INSTALLATION. I BECAME AWARE OF THE INCIDENT ON THE EVENING OF OCT/XF/08. I WAS INFORMED BY MY CO-WORKER OF THE INCIDENT; TELLING ME THAT ACFT WAS GNDED AND DELAYED IN ZZZ1 BECAUSE OF A MISSING CRASH AX BEHIND THE FO'S SEAT. TO THE BEST OF MY KNOWLEDGE; THE ACFT WAS DELAYED FOR A POSSIBLE 4 HRS UNTIL A CRASH AX COULD BE INSTALLED AND THEN THE ACFT WAS RELEASED. THERE WERE POSSIBLE EVENTS THAT MIGHT HAVE OCCURRED -- SUCH AS BEING LACK OF COM; POOR LIGHTING; AND DISTR OF THE WORKPLACE. I FEEL THE COM BTWN CO-WORKERS AND BETTER CONCENTRATION WOULD HELP TO PREVENT THIS TYPE OF INCIDENT FROM HAPPENING AGAIN; FOR ALL THE MANUALS AND PROPER PROCS WERE FOLLOWED; THE CHKS AND BALANCES WERE BROKEN DOWN THE LINE SOMEWHERE. SUPPLEMENTAL INFO FROM ACN 809610: WE NEGLECTED TO REMOVE THE OLD CRASH AX FROM THE OLD SEAT AND PUT IN THE NEW SEAT. ON OCT/XA/08 WHEN ACFT WAS AT THE GATE; IT WAS DISCOVERED BY THE FLT CREW THAT THE CRASH AX WAS MISSING BEHIND THE FO SEAT. SINCE THE CRASH AX WAS MISSING; THEY WERE AT THE GATE. THEY HAD TO AOG A CRASH AX FOR IT. THE EVENT OCCURRED BECAUSE THE CRASH AX WAS NOT INSTALLED BACK IN THE NEW SEAT AFTER THE CHANGE. I WAS WORKING WITH MY FELLOW MECH AND I DID NOT MENTION WHAT IT SAYS IN THE AMM TO XFER THE CRASH AX INTO THE NEW SEAT. EVEN THOUGH I DID NOT SIGN THE INSTALLATION; I WAS INVOLVED INSTALLING THE SEAT ALSO. BETTER COM BTWN THE PARTIES INVOLVED. MECHS DOING THE JOB AND INSPECTOR. ALSO; WE SHOULD HAVE 3 SIGNATURES FOR THE SEAT. 2 FOR THE MECHS; BECAUSE USUALLY 2 DOING THE TASK; AND ANOTHER FOR THE INSPECTOR. I FEEL JUST AS RESPONSIBLE FOR THE INCIDENT EVEN THOUGH MY SIGNATURE IS NOT THERE. I ALSO FEEL THAT THEY ARE VERY PROFESSIONAL AND NEVER THOUGHT THEY WOULD MISS THIS.